In the field there is a well known problem which is due to fertilizing soil with large amounts of plant nutrient. In that case the nutrient may dissolve into the soil at a rate which is too fast compared to the rate at which the nutrient is absorbed into the plants and improve their growth. Too high a solubility can lead to the leaching of large amounts of nutrient away from the roots or to the damage of plants due to overdosing of nutrient. One has tried to overcome the above disadvantages either by reducing the solubility of nutrients and/or by using barrier layers or coatings.
One way to bring about a slowly soluble fertilizer is to prepare an emulsion which has a non-hygroscopic component evenly surrounding the nutrient and preventing the nutrient from dissolving too early into the soil. The U.S. Pat. No. 3,192,030 discloses the mixing of solid nutrient to a so-called water-in-oil emulsion (w/o emulsion), the oil phase of which consists of an organic solution containing wax and the water phase of which consists of pure water. According the publication the formulation turns into solid, wax coated nutrient in the soil after the water and the organic liquid have evaporated, and the nutrient is slowly released to be exploited by the plants.
The U.S. defensive publication T969,003 discloses an emulsion composition which consists of a liquid plant nutrient, an organic solvent which is insoluble in water and w/o type surfactant. The mixture consists of about 13-26% by weight of fertilizer, about 60-81% by weight of water, about 4-13% by weight of oil and about 0.2-1.4% by weight of w/o type surfactant (examples 4, 6 and 7). The formulation thus concerns liquid fertilizer compositions where the plant nutrient is dissolved in a large quantity of water. The amount of fertilizer is very large and difficult to handle considering its nutritive value, and besides, it's use depends on transportation, treatment and spreading equipments of the liquid.
It is evident that although the arrangement of the U.S. publication T969,003 has many advantages e.g. its small number of components, it contains limitations concerning the handling and choosing of raw materials.